Determine Angle Between 2 Vector Equation Lines

$L_1=[2,2]+s[-1,3]$ $L_2=[5,1]+t[3,4]$ To get the acute angle, do the dot product $\vec{a}\cdot \vec{b}=|\vec{a}||\vec{b}|\cos \theta$ $\cos \theta =\frac{9}{5\sqrt{10}}$ $\theta =55.3^o$ The obtuse angle would be $\theta =124.7^o$